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26
<br />COPEIA, 1990, NO. 1
<br />Tyus, 1984; USFWS, unpubl.). However, there
<br />have been few studies investigating interactions
<br />between small introduced fishes and young P.
<br />lucius.
<br />This study evaluated behavioral interactions
<br />between age-0 P. lucius and six similar-sized
<br />species (native and non-native) which co-occur
<br />in backwater habitats. We hypothesized that di-
<br />rectinteraction between these introduced fishes
<br />and P. lucius would cause P. lucius to shift spa-
<br />tiallyand so reduce their ability to capture food
<br />items. We evaluated patterns of space use, ag-
<br />onistic behavior, and activity of seven fishes in
<br />species pairs, each pair containing P. lucius.
<br />METHODS
<br />Experimental design.-We collected 200 fishes
<br />by seining shoreline backwater habitats of the
<br />Yampa and Green rivers, Colorado and Utah,
<br />Oct.-Dec. 1986. Fishes selected for study in-
<br />cluded 50 native P. lucius (x = 50 mm TL, range
<br />= 38-72 mm TL) and 10 native Catostomus lati-
<br />pinnis (flannelmouth sucker) (x = 58 mm TL,
<br />range = 53-66 mm TL). Non-native fishes in-
<br />cluded 10 Pimephales promelas (fathead minnow)
<br />(x = 53 mm TL, range = 36-59 mm TL), 10
<br />Richardsonius balteatus (redside shiner) (x = 46
<br />mm TL, range = 43-56 mm TL), 10 Notropis
<br />lutrensis (red shiner) (x = 50 mm TL, range =
<br />41-61 mm TL), five Lepomis cyanellus (green
<br />sunfish) (x = 51 mm TL, range = 31-68 mm
<br />TL), and five Ameiurus melas (black bullhead) (x
<br />= 70 mm TL, range = 62-87 mm TL). Indi-
<br />vidual fishes of similar size were selected for
<br />study from the holding tanks; however, the
<br />above TL measurements were taken at study
<br />completion to avoid stressing the fish at study
<br />initiation. Fishes used included both young of
<br />larger species (e.g., Ptychocheilus lucius, C. lati-
<br />pinnis, A. melas, L. cyanellus) and adults of small-
<br />er species (e.g., N. lutrensis, R. balteatus, Pime-
<br />phales promelas). Species selection was based on
<br />similarity in habitat use and availability, and also
<br />included species that have been implicated in
<br />the literature as potential competitors or pred-
<br />ators of young Ptychocheilus lucius.
<br />We conducted experiments in Feb. and March
<br />1987 at the USFWS field station in Vernal, Utah.
<br />A total of six, 110 liter aquarium tanks were
<br />gridded with a 4 x 3 matrix (12 cell) to quantify
<br />fish location. We covered each tank on three
<br />sides with black plastic to prevent visual contact
<br />of specimens in adjacent tanks. White fluores-
<br />cent lights connected to an automatic timer were
<br />used to simulate a 12L/12D photoperiod. These
<br />switched on at 0600 h (day) and off at 1600 h
<br />(night). Red lights were used continuously so
<br />that the observer could view fishes at night.
<br />We divided the day into four equal observa-
<br />tion periods: dawn (0600 h), noon (1200 h),
<br />dusk (1600 h), and midnight (2400 h). Fishes
<br />were fed at 1200 h and 2400 h to compare
<br />feeding and nonfeeding behaviors. Foods in-
<br />cluded live brine shrimp (Anemia spp.) (3 ml)
<br />added via pipette and commercial trout chow
<br />(1 cc). These foods became widely dispersed in
<br />the tank shortly after addition. We added de-
<br />hydratedbrine shrimp (1 cc) and tubifex worms
<br />(1 cube/tank) to tanks after completion offeed-
<br />ingtrials as a dietary supplement. All tanks were
<br />maintained by undergravel filtration systems.
<br />Water temperature fluctuated with room tem-
<br />perature (x = 22 C, range 19-24 C), and average
<br />temperatures (22 C) were close to temperature
<br />preferenda of young P. lucius (i.e., 25 C; Black
<br />and Bulkley, 1985a, 1985b).
<br />Following a 1-3 mo acclimation period, we
<br />divided tanks in half with an opaque, porous
<br />partition and the following species pairs were
<br />established: Tank 1: 10 P. lucius/10 C. latipinnis
<br />(9 fish/10 m~), Tank 2: 10 P. lucius/10 Pime-
<br />phales promelas (9 fish/10 mp), Tank 3: 10 P.
<br />lucius/ 10 N. lutrensis (9 fish/ 10 m4), Tank 4: 10
<br />P. lucius/10 R. balteatus (9 fish/10 m~), Tank 5:
<br />5 P. lucius/5 A. melas (4.5 fish/10 m~) and Tank
<br />6: 5 P. lucius/5 L. cyanellus (4.5 fish/10 m2).
<br />Tanks 5 and 6 were established with fewer fish
<br />because we were unable to obtain 10 similar-
<br />sized individuals of both L. cyanellus and A. me-
<br />las. The behavior of P. lucius in the tank con-
<br />taining C. latipinnis was used as the baseline or
<br />"control" in the statistical analyses, rather than
<br />a tank containing only P. lucius, because we
<br />wished to compare behavioral attributes of
<br />young P. lucius when in a tank with a naturally
<br />occurring species, to that in tanks containing
<br />non-native fishes. We assumed there would be
<br />little interaction between similar-sized C. lati-
<br />pinnis and P. lucius because of different feeding
<br />;and space use habits (Jacobi and Jacobi, unpubl.
<br />ms.), and felt that this combination would serve
<br />as a good basis for comparing other interspecific
<br />behaviors.
<br />We removed partitions following a 15 d ac-
<br />climation period, and initiated observation of
<br />mixed species pairs shortly thereafter. Vertical
<br />distribution patterns were evaluated by record-
<br />ingfish location at 0600 h, 1200 h, 1600 h, and
<br />
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